Catastrophic pipe failures

The initiating event corresponds to a leakage in any mechanical equipment, pipe or flange, located between the vacuum column C-201 and the decomposition reactor E-207, as shown in Figure 6. Since the pipeline will be under severe conditions of acidity, pressure and temperature, an occurrence frequency of 5.23E-5/year is assumed, which is the generic value for catastrophic pipe failure (including straight pipe and connections) (Bari, 1985). 

Four Case Histories of Catastrophic Pipe Failures... 

Four case histories of catastrophic pipe failures... 

The analyses that have been used by the commercial nuclear power industry, subject to NRC approval on a case by case basis, make use of the LBB concept to justify exclusion of the dynamic effects of postulated pipe rupture. This concept is based on the ability to detect a fluid system leak- and perform an orderly and controlled plant shutdown before any potential exists for catastrophic pipe failures. Thus, the object of applying the LBB concept is to establish that a postulated crack remains stable under normal operating plus faulted loads or that significant margin exists against unstable crack growth if the postulated crack is predicted to grow with the applied loads. 

The exact cause of piping failure was not identified however, a gas cloud that covered a large area ignited, resulting in a 1,200-ft. (360 m) fireball. This started a chain of problem.s which resulted in BLEVEs or ruptures of four spheres and 44 cylindrical tanks. Some tanks weighing up to 20 tons skyrocketed and landed 3,900 ft. (1,200 ni) away. Reports indicated 542 people were killed in this catastrophe, 4,248 were injured, and about 10,000 were left homeless. Unofficial estimates of human sufloring were 129,21]... 

A fuel leak from the fuel supply pipework is foreseeable. It may arise following assembly, either when new or following maintenance, since the fuel pipework is routinely dismantled for turbine maintenance at intervals of one to three years. Gas turbines should operate without excessive vibration, and vibration detectors are often, but not always, fitted to larger units to detect bearing failmre. Such vibration could also cause fuel pipe joint failure. Catastrophic, sudden guillotine, pipe failure is very improbable, but a fuel leak from a control valve, flexible pipe, or flanged, screwed or welded pipe joint is a hazard against which appropriate precautions should be taken. 

BLEVEs (Boiling Liquid Expanding Vapor Explosions) A pressurized tank of VCM or associated piping exposed to an external fire may fail due to metallurgical weakening. Such failure may result in a catastrophic tank failure, a fireball and the potential for rocketing fragments. Relief valve overpressure protection will not prevent a BLEVE. 

Liquid-Metal Corrosion Liquid metals can also cause corrosion failures. The most damaging are liqmd metals which penetrate the metal along grain boundaries to cause catastrophic failure. Examples include mercury attack on aluminum alloys and attack of stainless steels by molten zinc or aluminum. A fairly common problem occurs when galvanized-structural-steel attachments are welded to stainless piping or eqmpment. In such cases it is mandatoty to remove the galvanizing completely from the area which will be heated above 260°C (500°F). 

BLEVE types of incidents arise from the reduction in yield stress of a vessel or pipe wall to the point that it cannot contain the imposed stresses by the design and construction of the container and are also influenced by the relief valve set point. This results in a sudden catastrophic failure of the containment causing the violent discharge of the contents and producing a large intense fireball. 

Ruptures or Internal Vessel Explosions - An catastrophic opening of a container (i.e., tank, vessel or pipe), commonly from overpressure or metallurgical failure, resulting in the immediate release of its contents. 

Pump and compressor seal areas are by far the most common areas where vapor releases may occur. This is followed by instrumentation sources, valve seals, gaskets and sample points and the most rare but usually catastrophic erosion and corrosion failures of process piping. 

Failure occurs when the component ceases to perform its required function. In the case of catastrophic failure, such as the rupture of a pipe or electrical breakdown of an insulator, this is obvious, but in many cases there is no such clear end of life. For example, is the end point when a small amount of environmental stress cracking has occurred, or when cracks have reached 5 mm in length Broadly, the definition of end point is that a property has reached a level at which safety, performance or market acceptance dictate that the component or product can no longer be used. 

These methods include estimating failure rate data using models or correlations developed from an engineering or scientific analysis of the influences on the reliability of particular types, classes, or groups of equipment. For example, Thomas provides a factor-based technique for estimating the probability of catastrophic leakage from a pipe or pressure vessel. Factors include size and shape influences, weld zones, facility age, and other quality factors (CCPS, 2000). 

Environmental stress cracking (ESC), usually associated with SCG accelerated by surfactants or other aggressive media, is also of considerable interest in its own right, since pipe materials are often intended for service in contact with water or other industrial fluids. Oxidative degradation is another important concern, particularly at high temperatures, and stabilisers are often added specifically to retard SCG and catastrophic failure [65, 66, 67, 68], the stabiliser type and concentration being critical at very low SCG rates, even where they have little effect on rapid fracture [69]. 

The third example describes mistakes made during the design, procurement and construction of a high-pressure steam piping system, resulting in a catastrophic failure of a pipe connector, due to chloride stress corrosion cracking. 

The failure investigations described in this paper illustrate two situations where human error during common maintenance and repair activities ultimately played a role in the failure of industrial machinery. The third failure investigation revealed how, even when the potential for failure is known (i.e., SCC of 304 SS), human error during the procurement and/or installation phase of the piping clamps resulted in an SCC-susceptible material being installed and ultimately failing in a catastrophic manner. 

The most important materials failure to avoid in the design of metal equipment is sudden catastrophic failure. This occurs when the material fractures under impulse instead of bending. Catastrophic failure can cause complete destruction of piping or equipment, and can result in explosions, huge spills, and consequent fires. Causes of some of the more common types of catastrophic failures are ... 

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